Angiosperms. Fertilization in flowering plants Causes of damage to the ovary
Fertilization
Female sex cell(gamete) is called egg. Pestle
Male sex cell(gamete) is called sperm. Stamen
Pollen composed of pollen grains. pollen grain
Vegetative
generative sperm
pollen tube The structure of the ovule: Chromosomes
First sperm double.
zygote.
Second sperm triple.
Endosperm
From the shells of the ovule seed coat is formed. From the walls of the ovary
double. Navashin S.G. In 1898. Thus, a fruit is formed, which consists of a seed and a pericarp.
The formation of the ovule.
A cavity appears in the middle of the primary tubercle, and ovules will form on its inner wall.
The ovules of angiosperms are similar in structure to those of gymnosperms, i.e. it is a megasporangium (nucellus), dressed in integuments, one of whose megaspores germinates into a female gametophyte. These ovules go through several stages of development. At first they are very tiny, in the form of a bulge of meristem cells. These are nucellus cells. Further, in the middle of the nucellus, one cell stands out in size - this is an archesporial cell, which subsequently divides by meiosis and 4 megaspores arise.
Nucellus by this time will increase in size and outside will be dressed (overgrown) with covers - integuments.
Of the 4 megaspores, only one will germinate into the female gametophyte, while the other 3 will be crushed and disappear (obliterate).
In the ovary, the formation of ovules takes place, the stigma catches and retains pollen grains on its surface, the style conducts male gametes to the ovules that arise during the germination of pollen grains.
By the time the development of the ovule is completed, the ovary becomes large, green, and on the cross section you can see that it consists of two structures: the walls of the ovary and the ovules.
The walls of the ovary are part of the green carpel and anatomically have a leaf structure, i.e. outer and inner epidermis, and between them green pulp - mesophyll cells.
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In angiosperms, the reproductive organ is the flower. Consider the processes occurring in stamens and pistils.
The formation of pollen grains occurs in the stamens. The stamen consists of a filament and an anther. Each anther is formed by two halves, in which two pollen chambers develop - microsporangia. The nests contain special diploid microsporocidal cells.
Each microsporocid undergoes meiosis and produces four microspores. Inside the pollen nest, the microspore increases in size.
7. Ovules in plant flowers develop in A. stigma of pistil B
Its nucleus divides mitotically and two nuclei are formed: vegetative and generative. A strong cellulose shell with pores is formed on the surface of the former microspore. Pollen tubes grow through the pores. As a result of these processes, each microspore turns into a pollen grain (pollen) - a male gametophyte. A mature pollen grain consists of two (vegetative and generative) or three (vegetative and two sperm) cells.
The formation of the female gametophyte (embryo sac) occurs in the ovule, which is located inside the ovaries of the pistil.
The ovule is a modified megasporangium protected by integuments. At the top of it there is a narrow channel - the pollen entrance. Near the pollen entrance, a diploid cell begins to develop - a megasporocyte (macrosporocyte). It divides by meiosis and produces four haploid megaspores. Three megaspores are soon destroyed, the fourth most distant from the pollen entrance develops into the embryo sac.
The embryo sac is growing. Its nucleus divides three times by meiosis. As a result, eight daughter nuclei are formed. They are located in four groups in two groups: one is near the pollen entrance, the other is at the opposite pole.
Then, one nucleus departs from each pole to the center of the embryo sac - these are polar nuclei. They can merge to form one central core. At the pollen entrance there is one egg and two cells of the synergid.
At the opposite pole - antipodal cells that are involved in delivery to the cells of the embryo sac nutrients and then disappear. Such an eight-core embryo sac is a mature female gametophyte.
Pestle. In the center of the flower is one or more pistils, usually pitcher-shaped or bottle-shaped.
In most pistils, one can distinguish the ovary - the main lower expanded part, which is strongly narrowed at the top into a column, forming a stigma at the top.
Ovary- a slightly enlarged, sometimes swollen part of the pistil, in which the ovules are located (seeds are formed from them after fertilization). If the ovary is attached to the receptacle only by its base, the rest of it is free, then it is called top(potato, tomato).
bottom(cucumber, pumpkin).
sedentary(poppy).
The megasporophyll grows together at its edges, forming a moist chamber that protects the modified megasporangium - the ovule.
Pollen is perceived by the glandular surface of the suture at the site of fusion of the edges of the megasporophyll. The evolution of the pistil is associated with the formation of specialized parts - the stigma, style and ovary, with the formation of the pistil from several megasporophylls, with the appearance of the lower ovary.
carpel.
Gynoecium
The ovules in the flowers of plants develop in
The gynoecium is called: apocarpous monocarp, cenocarpous - carpels 2 or more, they coalesce into one pistil (onion, potato, poppy).
With a cenocarpous gynoecium, the ovary cavity can be divided into nests according to the number of carpels (Fig. 5).
placenta.
The placenta is located at the site of fusion of the edges of the carpels. There are angular, central (columnar) and parietal placentation.
pedicel.
nucellus, integuments.
micropyle. chalazoy(Fig. 6).
Rice. 6 The structure of the ovule with the embryo sac:
direct, reverse And bent.
Megasporogenesis- formation of haploid megaspores by meiotic division. At the micropylar end, a megaspore mother cell (usually one) is laid. As a result of meiosis of this diploid cell, four haploid megaspores are formed. Three of them die off, one (usually the lower one, located farther from the micropyle) grows into a female gametophyte.
The female gametophyte is the embryo sac, formed by three successive mitotic divisions.
After the first division of the haploid nucleus of the megaspore, two nuclei are formed. They diverge towards the poles of the elongating megaspore, a large vacuole appears between them.
These polar nuclei combine to form a diploid nucleus called central, or secondary, nucleus of the embryo sac.
One of the three cells will ovum, the other two are synergists(auxiliary cells).
antipodes.
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Pestle. In the center of the flower is one or more pistils, usually pitcher-shaped or bottle-shaped. In most pistils, one can distinguish the ovary - the main lower expanded part, which is strongly narrowed at the top into a column, forming a stigma at the top.
Ovary- a slightly enlarged, sometimes swollen part of the pistil, in which the ovules are located (seeds are formed from them after fertilization).
If the ovary is attached to the receptacle only by its base, the rest of it is free, then it is called top(potato, tomato).
If the ovary is immersed in the receptacle with which it fuses, then such an ovary is called bottom(cucumber, pumpkin).
The column departs from the top of the ovary. It ensures that the stigma is carried upwards to a position favorable for trapping pollen. The stigma serves to perceive pollen, releases substances that contribute to its germination (sugars, lipids, enzymes). In the absence of a column, the stigma is directly adjacent to the ovary, in which case it is called sedentary(poppy).
The origin of the pistil is associated with the evolution of megasporophylls of ancient gymnosperms.
The megasporophyll grows together at its edges, forming a moist chamber that protects the modified megasporangium - the ovule. Pollen is perceived by the glandular surface of the suture at the site of fusion of the edges of the megasporophyll. The evolution of the pistil is associated with the formation of specialized parts - the stigma, style and ovary, with the formation of the pistil from several megasporophylls, with the appearance of the lower ovary.
The megasporophyll of angiosperms is called carpel.
Gynoecium- a set of carpels (megasporophylls) of a flower.
The gynoecium is called: apocarpous when there are 2-3 or more carpels in a flower, each of them forms an independent pistil (buttercup, wild rose); monocarp, when there is one carpel in the flower, forming one pistil (pea); cenocarpous - carpels 2 or more, they coalesce into one pistil (onion, potato, poppy). With a cenocarpous gynoecium, the ovary cavity can be divided into nests according to the number of carpels (Fig.
Rice. 5 Types of gynoeciums: a - apocarpous of three carpels; b, c, d - cenocarpous of three carpels: 1 - carpel; 2 - placenta; 3 - ovule
The place of attachment of the ovules to the wall of the ovary is called placenta. The placenta is located at the site of fusion of the edges of the carpels. There are angular, central (columnar) and parietal placentation.
Ovule, formation of megaspores and embryo sac. The ovules develop on the inner wall of the ovary, on the placenta.
The ovule is attached to the placenta pedicel.
The ovule consists of the multicellular nucleus of the ovule, or nucellus, and the two coverings surrounding it, or integuments.
Above the top of the nucellus, the integuments do not grow together, a microscopic channel is formed - the pollen entrance, or micropyle. The part of the ovule opposite the micropyle, from where the integuments depart, is called chalazoy(Rice.
The structure and development of the ovule of plants
6 The structure of the ovule with the embryo sac:
1, 2 – inner and outer integuments; 3-ovum; 4 - embryo sac; 5 - nucellus; 6 – chalaza; 7-antipodes; 8 - secondary nucleus; 9 - synergides; 10 – funiculus; 11 - placenta; 12 - conducting beam; 13 - pollen entry (micropyle)
Ovules are of three types: direct, reverse And bent.
In the direct ovule, the nucellus is a direct continuation of the seed stalk (the families Buckwheat, Nettle, Pepper), in the reverse, the nucellus is located at an angle to the seed stalk (most common), but the latter remains straight. In bent ovules, a bend is observed in both the nucellus and the pedicels (Leguminous, Marevy, Cabbage).
In the ovary there can be the most diverse number of ovules: in cereals - one, in grapes - several, in cucumber, poppy - many.
Nucellus is a true homologue of megasporangium; integuments arose later in the first seed plants.
In the nucellus, the ovule sequentially occurs: megasporogenesis, the development of the female gametophyte - the embryo sac, double fertilization, the development of the embryo and endosperm.
Megasporogenesis- formation of haploid megaspores by meiotic division. At the micropylar end, a megaspore mother cell (usually one) is laid.
As a result of meiosis of this diploid cell, four haploid megaspores are formed. Three of them die off, one (usually the lower one, located farther from the micropyle) grows into a female gametophyte.
The female gametophyte is the embryo sac, formed by three successive mitotic divisions. After the first division of the haploid nucleus of the megaspore, two nuclei are formed. They diverge towards the poles of the elongating megaspore, a large vacuole appears between them.
Then one nucleus from each quadruple moves to the center of the cell. These polar nuclei combine to form a diploid nucleus called central, or secondary, nucleus of the embryo sac.
The central nucleus is clothed with cytoplasm and becomes the central cell of the embryo sac (sometimes the fusion of the polar nuclei occurs later). Near the micropylar end of the embryo sac, an egg apparatus is formed from three cells that have arisen from three nuclei, around which the cytoplasm is concentrated.
One of the three cells will ovum, the other two are synergists(auxiliary cells).
Three cells develop at the chalazal end of the embryo sac antipodes.
The resulting embryo sac with seven naked cells is now ready for the fertilization process.
The embryo sac is the most strongly reduced female gametophyte.
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FERTILIZATION IN FLOWERING PLANTS
Fertilization- this is the process of fusion of male and female germ cells (gametes).
Female sex cell(gamete) is called egg. The ovules are produced in the ovules of the ovary. Pestle is the female reproductive organ.
Male sex cell(gamete) is called sperm. Sperm are produced in the anthers of the stamens.
Stamen is the male reproductive organ.
The anthers of the stamens contain pollen.
Pollen composed of pollen grains. pollen grain- this is one stick. Pollen grain contains 2 cells - vegetative and generative.
Vegetative is the cell that forms the pollen tube.
generative is the cell that produces two sperm.
sperm are the male sex cells.
In the process of pollination, the pollen grain falls on the stigma of the pistil, germinates and forms a pollen tube. pollen tube moves through the stigma, style into the ovary. In the ovary of the pistil are ovules (seed rudiments). They will develop into seeds. The structure of the ovule: ovule membranes, embryo sac, main ovum with a double set of chromosomes, central ovum with a single set of chromosomes.
help urgently) please 1. ovules in flowering plants develop in ... a) stigma
Chromosomes contain genes and are responsible for the storage and transmission of hereditary information.
The pollen tube carries 2 spermatozoa to the ovules and germinates into the ovule through the pollen entrance. Sperm have a single set of chromosomes.
First sperm fertilizes the main egg and the chromosome set becomes double.
As a result, a fertilized egg is formed, which is called - zygote. From the main egg and the first sperm, the embryo of a new plant is formed.
The structure of the embryo of a new plant: germinal root, germinal stalk, germinal leaves and buds.
Second sperm fertilizes the central egg and the chromosome set becomes triple.
As a result, endosperm is formed. Endosperm is a supply of nutrients that are necessary for the germination of the seed germ.
From the shells of the ovule seed coat is formed.
From the walls of the ovary the pistil is formed pericarp.
This fertilization of two eggs by two sperm is called double. It was discovered by Russian scientists Navashin S.G. In 1898.
Thus, a fruit is formed, which consists of a seed and a pericarp.
Male sex cells - sperm - are formed in the dust particles of pollen that develop in the anthers of the stamens of the flower. Usually, pollen consists of many dust particles (pollen grains) connected in groups. In dust particles, sperm are formed - male germ cells.
Female reproductive cells - eggs - are formed in the ovules located in the ovary of the pistil of the flower (flowering plants have ovaries with one or more ovules). In order for seeds to develop from all the ovules, it is necessary to deliver sperm to each ovule to the eggs, since each egg is fertilized by a separate sperm.
The process of fertilization in plants is preceded by pollination. As soon as a speck of dust hits the stigma of the pistil (with the help of wind or insects), it begins to germinate. One of its walls stretches and forms a pollen tube. At the same time, two spermatozoa are formed in the dust grain. They move to the tip of the pollen tube. Moving through the tissues of the stigma and style, the pollen tube reaches the ovary and penetrates into the ovule.
By this time, in the ovule, in its middle part, one cell divides and greatly elongates, forming the so-called embryo sac. In it, at one end is an egg, and in the center is a cell with two nuclei, which soon merge, forming one - the central nucleus. Having penetrated the ovule, the pollen tube germinates into the embryo sac, and there one sperm merges (combines) with the egg, forming a zygote, from which the embryo of a new plant develops.
Another sperm that has entered the embryo sac fuses with the central nucleus. The resulting cell divides very quickly, and soon a nutrient tissue, the endosperm, is formed from it.
The fusion in the embryo sac of sperm - one with the egg and the other with the central nucleus is called double fertilization.
The process of double fertilization is a phenomenon peculiar only to flowering plants. Thanks to double fertilization, the embryo of a new plant receives a very valuable endosperm with nutrients.
There is another classification:
13. Structure and functions of a flower.
Flower - reproductive organ of angiosperms. The flower consists of a pedicel, receptacle, perianth, androecium and gynoecium.
Fertile parts of a flower (stamen, pistil).
Sterile parts of the flower (calyx, corolla, perianth).
flower functions.
A flower is a modified shortened shoot adapted for the reproduction of angiosperms (flowering) plants.
The exclusive role of the flower is due to the fact that it combines all the processes of asexual and sexual reproduction, while in the lower and many higher plants they are divided. In a bisexual flower, micro- and megasporogenesis, micro- and megagametogenesis, pollination, fertilization, and the formation of seeds and fruits are carried out. The peculiarities of the structure of the flower make it possible to carry out the listed functions with minimal expenditure of plastic substances and energy.
The central (main) parts of the flower. Most plants have one or more pistils in the center of the flower. Each pistil consists of three parts: ovary - expanded base; column - more or less elongated middle part; stigma - the top of the pistil. Inside the ovary are one or more ovules. Outside, the ovule is surrounded by integuments through which a narrow channel passes - the pollen entrance.
Around the pistil (or pistils) are stamens. Their number in a flower is different in flowering plants: in wild radish - 6, in clover - 10, in cherry - a lot (about 30). The stamen consists of two anthers and a filament. Pollen develops inside the anther. Individual dust grains are usually very small grains. They are called pollen grains. The largest pollen grains reach 0.5 mm in diameter.
Perianth. In most flowers, the pistils and stamens are surrounded by a perianth. In cherries, peas, buttercups, the perianth consists of a corolla (a set of petals) and a calyx (a set of sepals). Such a perianth is called double. In a tulip, lily, lily of the valley, all the leaves are the same. Such a perianth is called simple.
Flowers with double perianth
Flowers with simple perianth
The tepals may grow together or remain free. In the tulip and lily, the perianth is simple, separate-leaved, and in the lily of the valley, it is joint-leaved. Flowers with a double perianth may also have fused sepals and petals. Primrose flowers, for example, have a calyx and a corolla. Cherry ranunculus flowers have a single-leaved calyx and a single-petaled corolla. The bell has a separate-leaved calyx, and the corolla has a joint-petal.
The flowers of some plants do not have a developed perianth. For example, in willow flowers, it resembles scales.
Inflorescences and flowers of willow
flower formula. The structural features of the flower can be noted in abbreviated form in the form of a formula. The following abbreviations are used in its compilation:
Ok - leaves of a simple perianth,
H - sepals, L - petals, T - stamens, P - pistils.
The number of flower parts is indicated by numbers in the form of an index (Ch5 is 5 sepals), with large numbers flower parts use the sign ∞. In the case of fusion of parts with each other, the number indicating their number is enclosed in brackets (L (5) - the corolla consists of 5 fused petals). If the parts of the flower with the same name are located in several circles, then a + sign is placed between the numbers indicating their number in each circle (T5 + 5 - 10 stamens in the flower are located 5 in two circles). For example, the lily flower formula- Ok3+3T3+3P1, bell- CH5L(5)T5P1.
Receptacle. All parts of the flower (near the flower garden, stamens, pistils) are located on the receptacle - the overgrown axial part of the flower. Most flowers have a pedicel. She moves away from the stem and connects it to the flower. In some plants (wheat, clover, plantain), pedicels are not expressed. Such flowers are called sessile.
Flowers bisexual and unisexual. Usually in one flower there are both pistil (pistils) and stamens. Such flowers are called bisexual. Some plants (willow, poplar, corn) have only pistil or stamens in the flower. Such flowers are called unisexual - staminate or pistillate (Fig. 71).
Monoecious and dioecious plants. In birch, corn, cucumber, same-sex flowers (staminate and pistillate) are located on one plant. Such plants are called monoecious. In poplar, willow, sea buckthorn, stinging nettle, some plants have only staminate flowers, while others have pistillate ones. These are dioecious plants.
The ovary is the empty lower thickened part of the pistil, the female reproductive organ of plants.
It provides protection and fertilization of ovules (ovules), from which seeds are formed.
The pistil is located in the flower and consists of the stigma, which traps the pollen, the style, through which the pollen enters, and the ovary, where the seeds develop. After fertilization, a fetus is formed from it.
In the central part of the ovule (nucellus) are eggs, in the case of pollination, they are fertilized, and seeds develop from them. In the same place, an embryo sac is formed, due to which they will feed.
Ovary functions
- Inside the ovary, the process of fertilization and seed maturation takes place;
- Protects ovules from external harmful environmental factors (temperature changes, drought, eating by insects, rain, etc.);
- Maintains the right level of moisture;
- Provides seed nutrition;
- It is the basis of the future fetus.
Ovary types
According to the number of nests, that is, the existing cavities separated by partitions in which the seeds are located, the ovary is single or multi-celled.
I - one-celled ovary, II - two-celled ovary, III - five-celled ovary. In all figures: 1 - ovary wall; 2 - nest; a - ovules, 4 - placenta.
Another classification of ovaries is based on their location in relation to the receptacle.
The receptacle is the lower part of the flower, that is, its base, on which the petals, sepals, stamens and pistils are located.
According to the type of location, the ovary can be:
- Upper or free - located above the receptacle. It does not grow together with other parts of the flower, while the flower is called pistillate (cereal, ranunculus, legume, etc.);
- The lower one is under the receptacle, the flower is attached to the top of the ovary, therefore it is called suprapestival (composite, cactus, orchid, etc.);
- Semi-lower - grows together with the flower, but not at the very top, the flower is called semi-pistillate (saxifrageous).
The formation of fruits from the ovary
Fruits, depending on the type of formation from the ovary, are divided into several types: 1. Real - are formed only by the ovary. Are divided into:
- Simple, formed by one pestle (cherry, plum, bird cherry, acacia bean);
- Complex, formed by several fused pistils (raspberries, blackberries)
- Fractional fruits are formed by a multi-celled ovary with partitions (forget-me-not, basil, lavender, thyme, etc.);
2. False - are formed with the participation of other parts of the flower, such as the receptacle and perianth, including petals and sepals.
note
It is easy to distinguish false ones from real ones by the remains of flower parts (apples, pears).
Causes of damage to the ovary
Damage to the ovary can lead to the absence of seeds and even fruits in the future. Damage can be caused by:
- Late spring frosts during flowering, in which the flowers and fruit set are showered. If the ovaries were partially damaged, then deformed, small, or unusable fruits develop from them;
- The absence or a small number of pollinators, while some of the flowers remain unfertilized, therefore they are discarded;
- Poor soil and lack of watering, when the plant does not have enough substances to grow all the ovaries that have appeared. In this case, it is necessary to apply complex mineral and organic fertilizers and provide watering during a drought;
- Pests (codling moth, apple sawfly, flower beetle, etc.). To get rid of them, you do not need to resort to artificial insect repellents, as they will also have a detrimental effect on pollinating insects. It is better to spray the plants with decoctions of herbs that repel pests (nettle, dandelion, garlic, wormwood, etc.)
- Leaf diseases. Healthy leaves are necessary to provide the plant with the necessary substances; without them, the ripening of fruits and seeds is impossible;
- Overloading with the number of fruits: with a large number of ovaries formed, the plant cannot feed them all, therefore it discards a part. Timely thinning of flowers will help to avoid this process.
